For seven years, Fox News has pushed back against the daily scrutiny and criticism leveled at it by Media Matters, the liberal watchdog group. But after founder David Brock said in March that his group’s new strategy amounted to a “war on Fox,” the network ratcheted up its response.

In the past 10 days, Fox has run more than 30 segments calling for the nonprofit group to be stripped of its tax-exempt status. Its Fox Nation website has even provided a link to pre-completed complaint forms against Media Matters to send to the Internal Revenue Service. (See also: Can Fox quash its fiercest critic? in The Arena)

While Fox News personalities like Glenn Beck and Bill O’Reilly have long grumbled about Media Matters, this attack on the group has been carried out across the channel’s news and opinion programs. It has included shows like “The O’Reilly Factor,” news coverage of the complaints to the IRS and even a psychological profile of Brock, a former conservative journalist who went over to the liberal side, on “Fox & Friends” that suggested he might be “full of self-hatred” because he was adopted.

“Media Matters is not a media investigative organization,” Fox News contributor and Washington Post columnist Charles Krauthammer said on “Special Report With Bret Baier” last week. “It’s a war on Fox. And you’re allowed to do that in a democracy. You can be as nasty as you want. The only thing is, don’t ask for a government subsidy.”

To get tax-free status, educational nonprofits have to support their claims with facts and refrain from directly engaging in politics — though they can be as ideological as they like. Fox argues that Media Matters has veered from that educational mission and should be stripped of its special status.

Its argument was first laid out in a June 22 column in the Washington Times by C. Boyden Gray, former President George H.W. Bush’s White House counsel, who cited two actions by Media Matters: its “unsupported” claims about Fox News being the voice of the Republican Party and a “sophisticated, Democratic-leaning media training boot camp” sponsored by the group that, Gray said, in essence, provided support to the Democratic Party.

“The declaration of war itself is a rhetorical device,” said Gray, a former Fox News consultant. “But when you go further and make allegations that are not substantiated, then it slips into, ‘Wow, this looks like it’s for and in support of the Democratic Party. … It’s absurd to say that Fox is the Republican Party. There’s no factual basis for that.’”

Ari Rabin-Havt, executive vice president of Media Matters, denies both allegations, pointing to the organization’s research on how Fox News, its employees and its parent companies “engaged in an unprecedented campaign in support of the Republican Party” during the 2010 election cycle.

“Our contentions about Fox News’s political operations are supported by the facts and their own actions, especially during the previous few years,” he said.

Regarding questions about the media training boot camp, profiled in a March 22 Washington Post story, Rabin-Havt said the training institute explicitly asks potential students whether they plan to run for office or work for a political campaign and declines to train them if they do.

“Our training institute trains progressive voices but not political ones,” he said. “We are not training candidates. We are not training political campaign employees.”

In both his column and his subsequent appearances on Fox News, Gray argued that the American Campaign Academy precedent provided a basis for probing Media Matters.

“It would obviously be highly discriminatory to allow tax-free donations to go to Democratic Party advocates when they are (properly) denied to Republican advocates,” he wrote.

Speaking to POLITICO, he went on to say that it was less the NRCC’s ties to the academy that violated the IRS rules than the fact that its graduates went on to work in Republican campaigns.

Even if Media Matters’s training is not explicitly designed to shape future Democratic campaign workers, he said, “I would be very surprised if you could identify trainees who end up in Republican campaigns.”

Rabin-Havt said those enrolled in the Media Matters boot camp are not being trained to participate in campaigns at all but to be media-ready progressive experts on issues like the BP oil spill.

This last point is of particular importance because of, perhaps, the most famous case in which the IRS denied tax-exempt status to a nonprofit educational organization over its political ties, which centered on the American Campaign Academy, a training institute spun off the National Republican Congressional Committee.

In 1989, a U.S. Tax Court judge upheld the IRS, saying that the academy was partisan because “its main purpose was to train campaign professionals for service in Republican entities and campaigns.” This violated part of the IRS rules requiring that nonprofit educational organizations not serve a purely private benefit.

Marcus Owens, a partner at Caplin & Drysdale and former director of the Exempt Organizations Division of the IRS, said the law is on Media Matters’s side on both counts.

On the training point, there would have to be proof of a direct tie to Democratic organizations, he said.

“If you can establish that the instructors and staff are working for the [Democratic National Committee], then you are getting closer to the American Campaign Academy,” he said. “But the fact that the students all have a certain orientation and then are going out and doing what they do with no lock step move into a political campaign, just makes it look a lot like a liberal college.”

And on the other, somewhat more vague point about whether Media Matters’s attacks on Fox violate the IRS’s rules about what tax-exempt educational organizations can say, he points to the criteria that the IRS laid out in 1986 for determining whether the method that an organization uses to come to its conclusions qualifies it as an educat entity.

First among these is that the organization not present “viewpoints or positions unsupported by facts” as “a significant portion of the organization’s communications.” Also on the list is a ban on “substantial use of inflammatory and disparaging terms” and conclusions made “on the basis of strong emotional feelings” rather than “objective evaluations.”

Owens argues that Media Matters is no different from its competitors on the right when it comes to these criteria.

“The bottom line is, as long as an organization is following a process and establishing or attempting to establish that its views have some basis in fact, then as long as it isn’t doing something like the equivalent of shouting fire in a crowded theater or encouraging people to commit crimes, then it probably is going to qualify as educational,” he said. “As a result, we have Media Matters, and we have Brent Bozell and the Media Research Center, and we have all kinds of other organizations that are doing the same thing.”

He argues that MRC’s website is not substantially different from Media Matters in that both attack media companies on what they feel is the opposite side of the ideological aisle.

“I’m afraid Fox loses this round,” Owens said.

When asked about the parallel, Bozell, president of the MRC, offered only the statement: “Media Matters stands accused of violating its tax-deductible status, and I think that fact speaks for itself.”

Owens emphasized that there is nothing in the IRS rules that prohibits tax-exempt educational nonprofits from attacking specific companies or from zeroing in on one company — as long as there is no private benefit to that company’s competitor — so Media Matters’s increasing focus on Fox News over the past few years does not trigger a violation.

Rabin-Havt argues that, in fact, the increased focus on Fox is simply an extension of Media Matters’s stated mission of educating the public about the distortions of conservative media.

“Over the past two years, if you look at the totality of our work, yes, absolutely the percentage of our work that has been devoted to Fox has risen and risen substantially,” he said. “That’s been a result of Fox being central to the conservative media infrastructure.”

Even the organization’s more aggressive stances, like its Drop Fox campaign to get advertisers to stop advertising on the network, he put within the frame of educating businesses about the media outlet they were supporting.

“Our goal is not to shut down Fox News,” he said. “Our goal is to change their behavior and to make them into a legitimate media organization.”